Ohituary Notices. 
Vll 
a telescope of no less than 28 inches aperture made by Sir Howard 
Grubb. Some years later Airy devised the “Orbit-Sweeper” — a 
new form of equatorial, with a third axis in the direction of what 
would be the tube in an ordinary equatorial. When properly set 
and driven by clockwork the telescope continues to sweep along any 
given great circle of the heavens. The University Observatory at 
Strassburg is provided with a beautiful instrument of this kind. 
The last considerable extension of the scope of Greenwich Obser- 
vatory made by the late Astronomer-Eoyal was the introduction in 
1873 of spectroscopy and the regular photography of solar pheno- 
mena. 
Of Sir George Airy’s many labours in fields outside the regular 
work of the observatory only the briefest mention can here be made. 
His eminently practical method of correcting the deviation of com- 
passes in iron vessels, the outcome of numerous experiments on 
board ship, came into general use. The determination of the density 
of the earth by experiments in Harton Colliery will long be remem- 
bered in the North Country. 
Of international as well as national importance was the share he 
took in the restoration of the standard weights and measures lost in 
the conflagration which destroyed the old Houses of Parliament. 
He took an active part too in the “ battle of the gauges,” which 
decided the width of railways in this country. Indeed, he may be 
said to have been general adviser on all matters connected with 
science not only to the government but to the whole country. He 
observed the total solar eclipse of 1842 in the north of Italy, and 
that of 1851 in Norway. To him astronomy is mainly indebted 
for the famous Eclipse Expedition to Spain in 1860, on which occa- 
sion the troopship “ Himalaya ” carried out a large party of observers, 
who, scattered along the line of total obscuration, shared in reaping 
perhaps the richest harvest of results ever secured on one of these 
rare occasions. 
The best-known books by Sir George Airy are the Mathematical 
Tracts, Gravitation, and &ix Lectures on Astronomy. For the 
Encyclopcedia Metropolitana he wrote a number of articles, notably 
those on “The Figure of the Earth” and on “Tides and Waves.” 
His contributions to the publications of learned societies were very 
numerous, no less than 242 papers standing under his name in the 
